1. Field of the Invention
The invention is based on a method of driving a plasma screen.
2. Description of the Related Art
It is known that, in the case of plasma screens, the individual plasma pixels are each driven individually in accordance with the picture content. This means that when there is a 16/9 picture present, and it contains 480 lines to be displayed, the division ratio results in a pixel number of 854 pixels per line if the pixel width is equal to the line height. In order to obtain a different luminous intensity in the case of a plasma screen, the plasma pixel has to be activated appropriately frequently. After such a plasma pixel has been activated, an extinguishing operation has to follow in order to make the plasma pixel dark. Given a division into 128 or 256 grey stages, that is to say 128 or 256 different luminous intensity values, at present the addressing of the picture is subdivided into so-called subfields.
Since the system is built up digitally, 8 subfields are used in the case of 256 grey stages. In the conventional method, in at 8 subfields in each case those pixel points which are needed to display different contours in a picture are addressed. This means that, in order to obtain a grey value of 256, the pixel point which is intended to reach this grey value must illuminate continuously, so that the value results from: subfield 1 equal to 1, subfield 2 equal to 2, subfield 3 equal to 4, subfield 4 equal to 8, subfield 5 equal to 16, subfield 6 equal to 32, subfield 7 equal to 64, subfield 8 equal to 128. This means that when the picture is displayed, each pixel point in each subfield would be addressed. If, for example, it is intended to reach a grey value of 64, this pixel point, which is to reach the grey value 64, is to be driven only in subfield 7. If a grey value of 72 is to be achieved, then the appropriate pixel point which is to achieve the grey value 72 has to be activated during the subfield 4 equal to 8 and the subfield 7 equal to 64. In the conventional method, in which the addressing for the entire picture is performed all at once, this has the disadvantage that there is a certain loss of time and, in addition, the luminous intensity levels of the individual cells are not very constant, since a relatively large amount of time is needed for the overall display of an entire picture, as a result of the overall addressing of the picture.
In addition to the method of the overall addressing of the picture and its subdivision into subfields, the method is also known in which addressing is carried out line by line, and each line is subdivided into 8 subfields in the case of 256 grey stages. In this case, it is also disadvantageous that time losses occur during the addressing and the activation of the cells.
The invention is based on the object of compensating for these time losses and of achieving an enhanced picture display. This object is achieved by the features of the invention specified in the claims. Advantageous developments of the invention are specified in the subclaims.
The method according to the invention for driving a plasma screen which is subdivided into horizontal lines and vertical pixel points, it being possible for the individual pixel points to be driven for different lengths of time, and a preparation mode and an addressing mode being provided for driving, is distinguished by the fact that the lines are combined into groups and in that, in the groups, a preparation mode and the addressing mode are executed separately, the preparation mode comprising a priming mode and an erasing mode.
This separation of the priming mode and addressing mode makes it possible to operate with the respectively optimal voltages. The priming mode is a ionization step which is necessary to insure a good firing of each cell. In the known methods, operations are carried out with an integrated circuit which executes both the priming mode and the addressing mode. In the method according to the invention, this is deliberately separated, in order that the circuit for the addressing can be supplied with a low voltage and the circuit for the preparation mode can be supplied with a higher voltage consequently needed. The separate circuits could be constructed as integrated circuits but could also be constructed discretely, so that, for example, an integrated circuit is used for the addressing, but a discrete circuit is used for the preparation mode. As a result of combining the lines into groups, it becomes possible for the system to execute the build-up of a screen more quickly, so that so-called picture flickering is improved and may even be dispensed with entirely.
Preferably, the preparation mode and the addressing mode will begin with an offset from line to line.
The fact that the preparation mode and addressing mode are offset from line to line means that the pixels are driven cyclically one after another, and the offset means that the picture as such is built up more uniformly.
In addition, in the groups, the preparation mode and addressing mode are subdivided into cycles.
The fact that, in the groups, the preparation mode and addressing mode are subdivided into identical cycles means that, on the one hand, in the groups the cycles can be executed in parallel and, on the other hand, as a result the picture will again appear to be more uniform.
Furthermore, the preparation mode comprises an extinguishing mode and/or a low-drive mode.
The preparation mode as such can be designed as an extinguishing mode, by the respective pixel point or the respective plasma cell being made dark, but can also be used to bring about low driving of the plasma cell. This low driving has the advantage that the plasma cell experiences better firing. After the plasma cell or the pixel has been ionized and then erased during the preparation mode, it can subsequently be addressed and then activated or not activated.
In the groups, the preparation mode and the addressing mode are executed separately.
Separate execution in the groups between preparation and addressing modes makes it possible for the complete groups to be ionized and erased and subsequently complete addressing of the groups to be carried out. It would thus be possible for discrete circuits to be used deliberately to extinguish all the lines or drive them low or, respectively, first to extinguish them and then to drive them low, and then for the individual lines to be addressed subsequently.
Furthermore, there is the possibility that in the method, in all the groups, the preparation mode and the addressing mode are executed synchronously.
Synchronous execution in all the groups would have the advantage that a simplification in circuit terms could be used, since the respective lines in the individual groups could be driven synchronously. A synchronous driving could lead to a further enhancement of the picture, the driving as such becoming somewhat more complicated. As a result of the respectively synchronous driving of the identical lines in the groups, a simplification would again occur, since the individual cycles in the individual groups are to be viewed in parallel.
Furthermore, in all the groups, the respective identical lines execute the preparation mode and the addressing mode synchronously.